1. Field of the Invention
The present invention relates to a packet distribution system, and more particularly to a packet distribution system for distributing packets to terminal devices on personal area networks that are connected by way of a plurality of communication links to a mobile network.
2. Description of the Related Art
As a means of forming private networks, we have seen in recent years the introduction of ad hoc networks that are configured by realizing direct asynchronous radio communication between terminal devices, or personal area networks (hereinbelow referred to as “PAN”) in which terminal devices that conform to the standards of IEEE 802.15 are connected by short-range radio such as Bluetooth.
One means of connecting these private networks to mobile networks is the protocol known as “Network Mobility (NEMO)” that is described in a non-patent document: Vijay Devarapalli, et al. “Network Mobility (NEMO) Basic Support Protocol” [online] June 2004, IETF (The Internet Engineering Task Force) Searched on Feb. 22, 2005. NEMO is a protocol for connecting a network that is constructed by the collection of a plurality of communication terminals to the Internet by way of mobile routers. The operation of NEMO is explained below with reference to FIG. 1 and FIG. 2.
NEMO is equipped with: Home Agent (communication terminal) 40, Home Agent (mobile router) 30, communication terminal 10, and mobile router 20. Referring to FIG. 1, the flow of control packets in NEMO is shown. Home Agent (communication terminal) 40 is a node for controlling communication terminal 10. Home Agent (mobile router) 30 is a node for controlling mobile router 20. When mobile router 20 receives a router advertisement from router 50 that is connected to Internet 500 and thus detects that it has moved to the subnet of prefix #1 (Operation A1), mobile router 20 uses prefix #1 to prepare a Care-of address (CoA), transmits a Binding Update to Home Agent (mobile router) 30 and reports the correspondence between the CoA and the Home Address (HoA) of mobile router 20 (Operation A2). Home Agent (mobile router) 30, having received the Binding Update, makes settings such that packets addressed to the home prefix of mobile router 20 are transferred to the CoA address of mobile router 20. When communication terminal 10 next receives a router advertisement from mobile router 20 and thus detects movement to the subnet of prefix #2, which is the home prefix of mobile router 20 (Operation A3), communication terminal 10 uses prefix #2 to prepare a CoA, transmits a Binding Update to Home Agent (communication terminal) 40, and reports the correlation between the CoA and the HoA of communication terminal 10 (Operation A4). Upon receiving the Binding Update, Home Agent (communication terminal) 10 makes settings such that packets addressed to HoA of communication terminal 10 are transferred to the address of CoA of communication terminal 10.
Next, FIG. 2 shows the flow of packets in NEMO. When packets are transmitted from communication partner terminal 60 to communication terminal 10, the packets are transmitted addressed to the HoA of communication terminal 10. Home Agent (communication terminal) 40, upon receiving the packets addressed to the HoA of communication terminal 10, tunnels to the CoA address of communication terminal 10 that has the home prefix of mobile router 20 and transfers the packets. Home Agent (mobile router) 30, upon receiving the CoA address of communication terminal 10, tunnels to the CoA address of mobile router 20 and transfers the packets. Mobile router 20, having received the packets, decapsulates the packets, and transfers the packets to communication terminal 10. Movement in a network is thus enabled in NEMO.
In mobile networks in recent years, users are not limited to using portable telephones as mobile terminals but have at their disposal a plurality of mobile terminals such as notebook computers and PDAs and use a variety of mobile terminals to fit particular purposes. As a consequence of this trend, when the above-described plurality of communication terminals is used to build a private area network, a private area network is formed that has a plurality of communication links with mobile networks. However, in a packet transfer method of the prior art such as NEMO, it is not possible to set a plurality of packet transfer paths to one mobile terminal that is present in a particular subnet in a Home Agent, and it is therefore not possible to simultaneously select a plurality of radio communication links to one communication terminal in a PAN and transfer packets.
Already existing communication links have various characteristics depending on the communication link, some links having an extensive communication coverage area but narrow communication bandwidth, as in W-CDMA, and other links having a scattered communication coverage area but a broad communication bandwidth. Thus, various links exist according to the nature of use of each application, W-CDMA being suitable as a communication link for cases in which the communication time is relatively lengthy and the communication bandwidth is narrow, as in VoIP, while a communication link having broad bandwidth such as a wireless LAN is suitable for an application for communicating in bursts of voluminous data such as the download of a music file. Preferably, a communication link that accords with the application is selected and packets transferred to a communication terminal in a PAN that is connected to a mobile network, and a plurality of communication links that accord with applications are simultaneously selected and packets transferred to one communication terminal in a PAN.